The general type and operating principles of PSA, or pressure swing adsorption, apparatus with which this invention is concerned are described in U.S. Pat. Nos. 3,564,816; 3,636,679; 3,717,974; 4,802,899; 5,531,807 and 5,871,564, the entire disclosures of which are incorporated by reference herein. For example, a pressure swing adsorption apparatus may include one or more adsorbers, each having a fixed sieve bed of adsorbent material to fractionate at least one constituent gas from a gaseous mixture by adsorption into the bed, when the gaseous mixture from a feed stream is sequentially directed through the adsorbers in a co-current direction. While one adsorber performs adsorption, another adsorber is simultaneously purged of its adsorbed constituent gas by part of the product gas that is withdrawn from the first or producing adsorber and directed through the other adsorber in a counter-current direction. Once the other adsorber is purged, the feed stream at a preset time is then directed to the other adsorber in the co-current direction, so that the other adsorber performs adsorption. The first adsorber then is purged either simultaneously, or in another timed sequence if there are more than two adsorbers, all of which will be understood from a reading of the above described patents.
When, for example, such an oxygen concentrator apparatus employing pressure swing adsorption is used to produce a high concentration of oxygen from ambient air for use in various applications, whether medical, industrial or commercial, air which enters the apparatus typically contains about 78% nitrogen, 21% oxygen, 0.9% argon, and a variable amount of water vapor. Principally, most of the nitrogen is removed by the apparatus to produce a gas product, which for medical purposes, for example, typically may contain at least about 80% oxygen.
As oxygen concentrator apparatus, particularly for medical uses, have become more compact and portable, and their users more mobile, we have found that the product gas oxygen concentration level is adversely affected by the humidity, moisture and/or relative water vapor concentration in the ambient air feed stream and particularly by operation, whether continuous or cycling, of the oxygen concentrator in close time proximity in high humidity and low humidity environments. Accordingly, there is a need for an improved oxygen concentrator apparatus configured to mitigate the adverse environmental effects on product gas oxygen concentration levels while maintaining a high level of portability.
It will be appreciated that for purposes of clarity and where deemed appropriate, reference numerals have been repeated in the figures to indicate corresponding features.